1. Field of the Invention
This invention relates to a disk apparatus which records and reproduces information in a disk-shaped medium.
2. Description of the Related Art
Recently, disk apparatuses such as magnetic disk apparatuses and optical disk apparatuses have been widely used as an external recording apparatus and an image recording apparatus of a computer.
Generally, magnetic disk apparatuses have a rectangular housing. Such a housing accommodates a magnetic disk serving as a magnetic recording medium, a spindle motor which supports and rotates the magnetic disk, a plurality of magnetic heads which write and read information in (from) the magnetic disk, a head actuator which movably supports the magnetic heads with respect to the magnetic disk, a voice coil motor which rotates and positions the head actuator, and a board unit having a head IC, etc.
Generally, the voice coil motor has a coil provided on a proximal end side of rotation of the head actuator, a pair of magnets arranged in positions to hold the coil therebetween, and a pair of yokes provided in correspondence with the respective magnets. The torque constant of the voice coil motor, which indicates a generated torque for a value of an electric current flowing through the coil, depends on magnetic flux density acting on the coil. For example, a generated torque is increased by reducing the magnetic gap between the pair of magnets and increasing the magnetic flux density, and thereby it is possible to provide a voice coil motor with good efficiency.
However, in the voice coil motor having the above structure, it is necessary to draw a lead for feeding a current to the coil through the magnetic gap, and thus it is difficult to reduce the magnetic gap to a satisfactory value. In comparison with this, a motor apparatus is proposed, in which magnets forming a magnetic gap are worked to have a recessed portion to let the lead through, and consequently the magnetic gap is reduced (for example, refer to Jpn. U.M. Appln. KOKAI Pub. No. 4-17678).
However, in the above apparatus, since a part of the magnets have to be cut away to form the recessed portion, the cost for manufacturing the motor is increased. Further, it is technically difficult to work the magnets.